A Systematic Review of Classical Entropy

It is difficult to grasp classical entropy because of the apparent complexity of relevant mathematics. Here we first give some physical thoughts on the concept of entropy, then examine its mathematical structrure. Several universal results are given by a set of equations governing the partial derivatives of internal energy and enthalpy, and applications are discussed with real gas models. This paper provides a systematic treatment of entropy beyond the ideal gas and may help understanding the foundation of thermodynamics.